1. Field of the Invention
This invention relates in general to signals processing, and more particularly to a method and apparatus for providing a read channel having imbedded channel signal analysis.
2. Description of Related Art
Recently developed data storage devices, such as magnetic disk drive devices (i.e., hard disk drives), have increased storage capacity and increased data access speed. With these advantages, magnetic disk drive devices have become widely used as auxiliary memory devices for computer systems. More generally, developments in pulse communications related to these improvements in disk drive technology have recently provided increased speed and reliability in a wide range of pulse communications systems.
The primary features of a magnetic disk drive device that affect storage capacity and access speed are the head, the recording medium, the servo mechanism, the signal processing technique used in the read/write channel, and the like. Among these, signal processing techniques utilizing PRML (Partial Response Maximum Likelihood) detection have greatly contributed to the increased storage capacities and high access speeds seen in modem magnetic disk drive devices.
Each read/write head generates or senses electromagnetic fields or magnetic encodings on the magnetic disk as areas of magnetic flux. The presence or absence of flux reversals in the electromagnetic fields represents the data stored on the magnetic disk. A flux reversal is a change in the magnetic flux on contiguous areas of the magnetic disk. The presence or absence of magnetic flux reversals correspond to binary 1's and 0's of a diagnostic input signal.
To “write” data onto a magnetic disk, electronic components receive data from a host device and translate the data into magnetic encodings. The head transfers the magnetic encodings onto a portion of the magnetic disk.
To “read” data from the magnetic disk, the head is positioned adjacent to the portion of the magnetic disk having the desired magnetic encodings. The head senses and transfers the magnetic encodings from the magnetic disk. The electronic components translate the magnetic encodings into the data, which is transferred to the host device. The host device may be a personal computer or other electronic equipment. The electronic components may apply error detection and correction algorithms to ensure accurate storage and retrieval of data from the magnetic disk. To improve data storage densities on disk drives, magneto resistive and inductive read/write heads have been developed with increased sensitivity to sense smaller amplitude magnetic signals and with increased signal discrimination.
The primary function of the disk drive read channel is to reliably recover data from a noise contaminated read back signal. State of the art detection architectures equalize to a fixed length partial response target and then use the Viterbi algorithm for detection. A read channel circuit includes components for initial processing of the analog read signal generated by the read/write head of the device. This processing typically includes automatic gain control (AGC) amplification, filtering, and equalization, as well as analog-to-digital conversion.
Channel customers are always interested in having imbedded solutions for signal measurement, analysis, tuning, and optimization. The read signal always contains some random noise. The read signal, and certain other signals produced by processing the read signal and that also contain noise, are referred to herein as noise-corrupted signals. For example, it is important to understand the noise contributions in a drive environment, the electronic Noise due to electronics in signal path and stationary Noise due to disk properties. In addition, transition jitter noise due to the boundary structure of written magnetic transitions and breathing mode noise due to variations in sharpness of written magnetic transitions may also be present. These are just a few types of noise that may be present in a read signal, but other types of noise may also be present.
To test the performance of a magnetic storage device, built-in test processes have been used. For example, test tracks having known recording patterns of encoded and precoded data values have been recorded on a data storage surface to determine the noise included in the read signal. These patterns are played back and passed to an on-drive error measurement circuit. Thus, an error generator may generate error value samples by calculating a difference between the nominal, expected value of the data sample, and the value of the data sample as read from the storage surface. The results of this test may be used to adjust e.g. write precompensation within the disk drive.
However, A non-embedded solution for noise analysis requires the high-speed acquisition of analog signals (or digital signals if available) and a great deal of off-line processing. Thus, an imbedded signal analysis tool would be very valuable. The high level of hardware integration and high speed & frequencies present in the drive environment could allow channel Parameters to be optimized based on noise analysis including media noise post-processor (MNP) settings and programmable NPML detection targets. Head and disk characterization could also be performed.
It can be seen that there is a need for a method and apparatus for providing a read channel having imbedded channel signal analysis.